Cape Breton County is a county in the Canadian province of Nova Scotia, on Cape Breton Island.

Taking its name from Cape Breton, the most easterly point of the island which was called after either the Bretons of England or the Bretons of Brittany, this municipality has what is probably the oldest surviving European name to have been used to designate part of North America. By proclamation of October 17, 1763 after termination of the Seven Years War, Cape Breton Island was formally annexed to Nova Scotia. For a time thereafter Cape Breton Island was part of Halifax County. On December 10, 1765 Cape Breton Island was set apart as a separate county.

From 1784 to 1820 Cape Breton Island was a separate colony with a Lieutenant Governor and a nominated Council, but without an elected house of assembly. Not until after Cape Breton was reannexed to Nova Scotia in 1820 did it get representation in a house of assemblv.

Although subdivided into three districts in 1824, Cape Breton County was co-extensive with Cape Breton Island from 1820 to 1835 when the county was divided into three separate and distinct counties - Cape Breton (Northeastern District), Richmond (Southern District) and Juste au Corps (Northwest District) later called Inverness.

In 1851 Victoria County was formed out of part of Cape Breton County and a year later, in 1852, the boundaries of Cape Breton County were redefined.

The boundaries of the county are also the boundaries of Cape Breton Regional Municipality plus the Indian reserves of Eskasoni and Membertou .